The metabolism of galactose by living organisms involves three enzymatic steps that convert galactose to glucose-1-phosphate, a major metabolic intermediate. In microorganisms, the synthesis of the enzymes of this pathway is inducible by galactose and other specific inducers and is controlled by a genetic mechanism which appears to be consistent with the operon model proposed by Jacob and Monod. The purpose of this work is to study the regulation of galactose metabolism in animals. The galactose enzymes will be purified and studied for feedback inhibition or activation and for other factors that might control their activity. Regulation of galactose metabolism will be examined by studying the influences of diet and hormones on the activity of the galactose enzymes in the liver. Coordinate regulation with the ratio of the activities of the galactose enzymes remaining constant under different conditions will also be investigated. Hopefully, this will broaden our understanding of the regulation of pathways in higher organisms and help clarify the differences between the regulation of pathways in higher organisms and in microorganisms.